DIATOMS 



All of the major diatom species in the upper Stillwater 

 River are either tolerant of a wide range of trophic conditions 

 from oligotrophic to eutrophic or exhibit their most vigorous 

 growth in stronger mesotrophic to eutrophic waters (Table 4) . 

 Among the tolerant species is Encyonema minutum, which dominated 

 the diatom assemblage below Daisy Creek. 



Diatom species richness and diversity were depressed at both 

 sites (Table 4) . Very low diversity and a large percentage of 

 Encyonema minutum indicated moderate impairment and partial 

 support of aquatic life uses below Daisy Creek. Above the 

 Wilderness boundary, impairment was minor and aquatic life uses 

 were fully supported. 



A relatively large number of teratological diatom cells also 

 indicates moderate impairment below Daisy Creek (Table 4) . 

 Abnormal valves were observed in Achnanthidium minutissimum and 

 Cocconeis placentula . The cause of these deformities is probably 

 heavy metals. The number of teratological cells was much smaller 

 above the Wilderness boundary, indicating only minor impairment. 



The disturbance index (% Achnanthidium minutissimum) 

 indicated minor impairment at both sites. Achnanthidium 

 minutissimum is tolerant of heavy metals and typically colonizes 

 recently scoured sites. Large numbers of this species indicate a 

 combination of chemical and physical disturbance at both sites. 



The pollution index indicated minor impairment from organic 

 loading below Daisy Creek and no impairment above the Wilderness 

 boundary (Table 4) . The source of the organic loading below 

 Daisy Creek is unknown, but it may be internal and result from 

 the in situ production of algal slimes. 



